The structural portion of the roof of many buildings includes a deck constructed of wood, concrete, steel or other structural materials. In order to waterproof the deck, it is necessary to apply a roofing membrane to the deck. One roofing membrane commonly utilized for roofs of minimum pitch, such as are commonly found on industrial and commercial buildings, is a built-up roof. A built-up roof comprises alternate layers of roofing felt and hot or cold asphalt.
Roofing felt is a flexible sheet material commonly provided in rolls. The felt may be constructed, for example, of a mat of asbestos, rag, fiberglass, etc. impregnated or coated with bitumen.
A primary problem with a built-up roof is in laying the roofing felt. One way to accomplish this is to unroll the felt by hand; however, this is a very time-consuming process. Various machines for unrolling the rolls of roofing felt have been proposed, but difficulty has been encountered in causing the machine to move along a perfectly straight line while unrolling the felt. Maintaining a straight line while unrolling a wide sheet of flexible material is always difficult, but the problem is made more accute with roofing felt because the rolls are often not cylindrical. In addition, if an incorrect line is established, it is difficult to unpeel the felt and begin anew due to the adhesive nature of the previously poured layer of asphalt.